As mountain bike suspension has evolved, several problems exist, some due to the unique requirements inherent in pedal powered vehicles that are required to perform in varied and diverse conditions. One of these problems is the desire to have different suspension characteristics while under power or forward acceleration (such as “anti-squat”, or in the particular case of the pedal/crank powered bicycle, to be firmer/stiffer while pedaling), especially while traversing smooth ground and/or climbing, when the rider weight bias is to the rear, while retaining the ability to absorb bumps when the wheel encounters a bump.
Another problem is to retain desirable suspension action while braking, especially when traversing a steep downhill section, where all the rider weight is toward the front of the bike, and the rear suspension is relatively unloaded. A different spring rate and/or compression and rebounding damping characteristics are desirable during these conditions.
Yet another problem is the conflicting frame geometry requirements of climbing versus descending. These conflicting frame geometry requirements are true of both suspension and non-suspension bikes such as road bikes. Typically, while climbing on a bicycle, a steep fork and seat tube angle (closer to vertical) are an advantage, not only to keep weight on the front wheel, (at a time when the rider's weight is naturally more to the rear), which aids steering control and prevents the unwanted “wheelie”, but also to position the rider more favorably over the pedals, for better power transfer, with less effort to stay over the cranks, which in turn allows better power transfer from the rider. Conversely, while descending and braking, a slack fork and seat tube angle (less vertical) are an advantage. This aids stability at a time when weight is unavoidably transferred to the front. This can also help minimize this weight transfer at a time when the rider's weight distribution is already tending toward the front due to the angle of descent.
Thus, regardless of the intended use of a bicycle, a different geometry is desirable for climbing and/or hard pedaling than would be optimum for descending and/or braking.
Several designs currently available attempt to solve some of these problems. Each of these designs has negative behavior associated with them. One such design is commonly called an “inertia valve” shock absorber or damper or “brain” type dampers/shock absorbers. The inertia valve shock attempts to separate forces trying to compress the rear wheel relative to the frame. It uses a weighted mass inside the shock that bounces up and down during use. The theory is that this mass will move, or be biased in one direction when the rear wheel encounters a bump, and move or be biased in the other direction when the frame is trying to compress relative to the wheel due to pedaling forces, or rider weight shifts. The orientation of this mass, or inertia valve, then engages an alternate damping characteristic. This approach is characterized by so-called “brain” dampers or shock absorbers.
A number of problems are associated with this design. First, the wheel has to encounter a bump before the mass changes position, meaning the wheel will have a delay when encountering a bump, before the mass can move. This delay causes an unresponsive wheel when reacting to the bump force. Further, the mass can move in the wrong direction at the wrong time, causing the damping characteristics to be less than desirable under certain conditions. This results in harsh ride quality and/or loss of wheel contact and traction with the ground. This design offers no improvement during braking, and suffers the same negative effects mentioned previously.
A second design employs what has become commonly referred to as “stable platform” valving, or damping or pedaling platform type dampers/shock absorbers. This strategy attempts to utilize a different damping characteristic in response to different input frequencies. The theory is that a pedaling input force, or rider weight shift, is characterized by a different input frequency than a bump force, and therefore allows a “stiffer” shock or damping characteristic for those pedaling forces. The main problem with this design is that some bump forces are indeed similar or the same frequency as the input forces caused by rider pedaling or weight shifts. This results in the stiffer characteristic to be present under certain bump conditions, causing the wheel to be unresponsive during those bumps. This results in a harsh ride quality and/or loss of wheel contact and traction with the ground. This design offers no improvement during braking, and suffers the same negative effects mentioned above.
A third type of design can be characterized by what is commonly referred to as a “virtual pivot”, “floating pivot”, “instant center” or similar designation. These terms generally describe a suspension design where the rear swingarm to which the rear wheel is attached, is connected to the frame by two other links. These other links are positioned to provide the rear wheel with a wheel path, and (bump and pedaling) force response characteristic that is associated with a pivot in space other than a physical pivot on the bicycle. The location of this effective pivot is a function of the lengths and angular orientation of these links.
The main problems with this type of design can include wheel path compromises, spring and damper progression compromises and problems associated with the fact that the effective pivot location moves when the rear wheel travels in compression or rebound, potentially causing negative effects. A further problem for these designs occurs when the links are arranged in such a way to provide an anti-lift force under braking, in an attempt to counteract the rider/frame forward weight shift that accompanies braking events. This anti-lift force causes the rear wheel to compress relative to the frame, preloading the spring into a higher force level. This causes the rear suspension to be unresponsive to bump forces while braking. This results in harsh ride quality and/or loss of wheel contact and traction with the ground. None of the above designs attempts to address the issues of varying suspension travel and frame geometry.
None of the foregoing designs addresses the issues of varying suspension travel and frame geometry.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.